Java集合知识总结
List集合知识总结:
List<String> books = new ArrayList<>();
books.add("疯狂Java讲义");
books.add("疯狂Android讲义");
books.add("轻量级Java web讲义");
list集合的形式:[疯狂Java讲义, 疯狂Android讲义, 轻量级Java web讲义]
List<Map<String,Object>> list1 :List集合的这种形式
[{ID=24, IDnumber=123456789632597, actualpayment1=0.0, actualpayment10=0.0, jobNo=102, name=郎咸平, partybranch=本部第五党支部, payable1=0.0, payable10=404.0, time=20180206 15:15:37, year=2018}]
c[i] = Float.parseFloat(list1.get(0).get("Payable"+i).toString()) -Float.parseFloat(list2.get(0).get("Payable"+i).toString());
List集合中实际上也是以key-Value形式存储的数据,当我们拿数据的时候,仍然可以根据key获得value
List集合中的数据用[]包含,Map中的数据用{}包含
用谷歌提供的gson包,将List集合转为json字符串:
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
System.out.println("将List转换为json字符串");
Gson gson1 = new GsonBuilder().setDateFormat("yyyy-MM-dd").create();
String s1 = gson1.toJson(books);
System.out.println(s1);
转化后的json字符串形式:["疯狂Java讲义","疯狂Android讲义","轻量级Java web讲义"]
将JSON字符串转为List集合:
Map集合知识点总结:
Map<String , List<String>> schoolsInfo = new HashMap<>();
List<String> schools = new ArrayList<>();
schools.add("斜月三星洞");
schools.add("西天取经路");
schoolsInfo.put("孙悟空", schools);
Map集合的形式:{孙悟空=[斜月三星洞, 西天取经路]}
用谷歌提供的gson包,将Map集合转为json字符串:
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
System.out.println("将Map转换为Json字符串");
Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd").create();
String s = gson.toJson(schoolsInfo);
System.out.println(s);
转化后的json字符串形式:{"孙悟空":["斜月三星洞","西天取经路"]}
将Map集合转JSON字符串,再将JSON字符串转为JSONObject对象
import net.sf.json.JSONObject;
需要的jar包:
commons-beanutils-1.7.0.jar commons-collections-3.1.jar commons-lang-2.5.jar commons-logging.jar ezmorph-1.0.3.jar json-lib-2.1-jdk15.jar
Map<String , List<String>> schoolsInfo = new HashMap<>();
List<String> schools = new ArrayList<>();
schools.add("斜月三星洞");
schools.add("西天取经路");
schoolsInfo.put("孙悟空", schools);
schoolsInfo.put("猪八戒", schools);
System.out.println(schoolsInfo);
Map集合的形式:{孙悟空=[斜月三星洞, 西天取经路]}
{孙悟空=[斜月三星洞, 西天取经路], 猪八戒=[斜月三星洞, 西天取经路]}
System.out.println("将Map转换为Json字符串");
Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd").create();
String s = gson.toJson(schoolsInfo);
System.out.println(s);
转化后的json字符串形式:{"孙悟空":["斜月三星洞","西天取经路"]
{"孙悟空":["斜月三星洞","西天取经路"],"猪八戒":["斜月三星洞","西天取经路"]}
System.out.println("将Map对应的字符串转化为JSONObject");
JSONObject jactupay =JSONObject.fromObject(s);
System.out.println(jactupay);
转化后的JSONObject:{"孙悟空":["斜月三星洞","西天取经路"]}
{"孙悟空":["斜月三星洞","西天取经路"],"猪八戒":["斜月三星洞","西天取经路"]}
System.out.println("将Map对应的字符串转化为JSONArray");
JSONArray array = JSONArray.fromObject(jactupay);
System.out.println(array);
转化后的JSONArray:[{"孙悟空":["斜月三星洞","西天取经路"]}]
[{"孙悟空":["斜月三星洞","西天取经路"],"猪八戒":["斜月三星洞","西天取经路"]}]
JSON字符串→JSonArra(Java对象)→Java实体类
JSON字符串→Map集合(Java对象)→Java实体类 可不可以还不知道???